JP2014054800A - Driving method of piezoelectric material, driving method of droplet discharge head, droplet discharge head, and image recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To substantialize a driving method of a droplet discharge head which reduces a load of a piezoelectric device and suppresses deterioration of an electromechanical conversion capability to further suppress variation of a displacement when recovering the displacement of the piezoelectric device whose displacement characteristic is deteriorated due to long time application of a driving voltage.SOLUTION: A first waveform F, whose electric field strength exceeds a coercive electric field of an electromechanical conversion film, is applied to a piezoelectric actuator, and then a second waveform R, whose polarity is reverse to the first waveform F and electric field strength is less than the coercive electric field and falling and rising are expressed by a sine wave, is applied thereto.

Description

  The present invention relates to a driving method of a piezoelectric body, a driving method of a droplet discharge head using the piezoelectric body, a droplet discharge head, and an image recording apparatus including the same.

The ink jet recording apparatus has many advantages such as extremely low noise and high-speed printing, and furthermore, an inexpensive plain paper having a degree of freedom of ink can be used. Therefore, it is widely deployed as an image recording apparatus or an image forming apparatus such as a printer, a facsimile machine, and a copying apparatus.
A droplet discharge head used in an inkjet recording apparatus or the like includes a nozzle hole that discharges an ink droplet (droplet) and a liquid chamber (discharge chamber, pressurized liquid chamber, pressure chamber, ink flow path) that communicates with the nozzle hole. And pressure generating means for discharging ink in the liquid chamber.
As the pressure generating means, an electro-mechanical conversion element (piezoelectric actuator), which is a piezoelectric element including a piezoelectric body, is used to piezo eject ink droplets by deforming and displacing the vibration plate forming the wall surface of the discharge chamber. What is called a mold is known.
In addition, the piezoelectric body used for the electromechanical conversion element has a property of generating electric charges when stress is applied and conversely expanding when an electric field is applied. A piezoelectric actuator is realized as an electro-mechanical conversion element that can be used in a droplet discharge head. As the piezoelectric body, for example, ternary metal oxide lead zirconate titanate or PZT can be used.
Piezo-type pressure generating means include longitudinal vibration (push mode) type using deformation (extension and contraction) in the d33 direction (axial direction of the piezoelectric element), and lateral vibration (bend mode / deflection) using deformation in the d31 direction. Vibration) type, and further, a shear mode type using shear deformation. Recently, a thin film actuator in which a liquid chamber and an electromechanical conversion element are directly formed on a Si (silicon) substrate has been devised due to advances in semiconductor processes and MEMS (Micro Electro Mechanical Systems).

By the way, when such a piezoelectric actuator is repeatedly used, a fatigue phenomenon occurs in the displacement of the piezoelectric body.
That is, since the polarization inside the piezoelectric body repeatedly rotates and expands during repeated driving, the polarization direction is partially fixed along the drive voltage application direction along with the formation of the internal electric field as the drive time elapses. It is a problem that it drops.
When the amount of displacement of the piezoelectric body decreases with time, the ink jet recording apparatus has a problem that ejection droplet characteristics such as ejection droplet volume and ejection droplet velocity are not stable.

Therefore, in order to recover the deteriorated displacement of the piezoelectric element, a method of destroying an internal electric field formed in the piezoelectric body by applying a voltage in the direction opposite to the driving voltage direction has been proposed.
For example, in Patent Documents 1 and 2, as a method for recovering a phenomenon in which the displacement characteristics (discharge droplet characteristics) of a piezoelectric element deteriorate due to long-term use (applied drive voltage for a long time), In addition, it is disclosed that an electric field higher than the coercive electric field is applied in a direction opposite to the driving voltage direction (reverse polarity), thereby destroying an internal electric field formed in the piezoelectric element and restoring displacement characteristics.

However, depending on the methods described in Patent Documents 1 and 2, since the strength of the voltage having the opposite polarity to the driving voltage applied to the piezoelectric element is greater than the coercive electric field of the piezoelectric element, the voltage direction of the driving waveform is reversed. There is a problem in that the electric charge and polarization are deviated in the direction and the displacement characteristics are deteriorated.
In view of such a problem, the present invention provides a piezoelectric body capable of recovering the displacement of a piezoelectric body in a piezoelectric element (piezoelectric actuator) whose displacement characteristics have been degraded by applying a drive voltage for a long time. The purpose is to propose a driving method.

  In order to solve the above problems, the invention of claim 1 is a method of driving a piezoelectric body that is deformed by application of a voltage, wherein the electric field strength of the piezoelectric body is higher than that of the piezoelectric body. And applying a second waveform having a pulse waveform having a polarity opposite to that of the first waveform and an electric field strength less than the coercive electric field after applying a first waveform exceeding Features.

  As described above, according to the present invention, there is provided a piezoelectric body driving method capable of recovering the displacement amount of a piezoelectric body whose displacement characteristics have been degraded by applying a driving voltage for a long time. It can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory perspective view of an ink jet recording apparatus to which a piezoelectric element as an electro-mechanical conversion element of the present invention is applied. FIG. 3 is an explanatory side view of a mechanism portion of an ink jet recording apparatus to which a piezoelectric element as an electro-mechanical conversion element of the present invention is applied. Sectional drawing which shows schematic structure of the droplet discharge head which concerns on this embodiment (the 1). Sectional drawing which shows schematic structure of the droplet discharge head which concerns on this embodiment (the 2). FIG. 4 is a diagram showing a processing system for driving a piezoelectric actuator in the droplet discharge head of the present embodiment. The schematic diagram which shows the relationship between an electromechanical conversion element, an upper electrode, and a lower electrode in a piezoelectric actuator. The figure which shows the typical PE hysteresis loop of the piezoelectric actuator 50 in the droplet discharge head of this embodiment. The figure which shows an example of the voltage waveform applied to the electromechanical conversion element by this embodiment. The graph which shows the relationship between the meniscus natural vibration period Tc and the reverse polarity waveform R. FIG. The graph which showed the evaluation result of the displacement fluctuation | variation in the electromechanical conversion element of this embodiment. The figure which showed the change rate of the displacement of the electromechanical conversion element of this embodiment. The figure which showed the displacement (b) of the diaphragm when the pulse of a reverse polarity is simply applied (a) and the meniscus natural vibration period is considered.

Embodiments of the present invention will be described below in detail with reference to the drawings.
The piezoelectric element as the electro-mechanical conversion element according to the present invention is applicable to a droplet discharge head and an image forming apparatus (inkjet recording apparatus) using the same.
FIG. 1 is a perspective explanatory view of an ink jet recording apparatus to which a piezoelectric element as an electro-mechanical conversion element of the present invention is applied, and FIG. 2 is a side explanatory view of a mechanism portion of the recording apparatus.
The ink jet recording apparatus shown in FIGS. 1 and 2 includes a carriage that can move in the main scanning direction inside the recording apparatus main body 1, a recording head that includes the ink jet head that implements the present invention mounted on the carriage, and supplies ink to the recording head. A paper feed cassette (or a paper feed tray) 4 capable of storing a large number of sheets P from the front side is housed in the lower part of the apparatus main body 1. It can be detachably mounted, and the manual feed tray 5 for manually feeding the paper P can be opened, the paper P fed from the paper feed cassette 4 or the manual feed tray 5 is taken in, After a required image is recorded by the printing mechanism unit 2, the image is discharged to a paper discharge tray 6 mounted on the rear side.

The printing mechanism section 2 holds a carriage 9 slidably in the main scanning direction by a main guide rod 7 and a sub guide rod 8 which are guide members horizontally mounted on left and right side plates (not shown). (Y), cyan (C), magenta (M), black (Bk) The ink jet head according to the present invention for ejecting ink droplets of each color of the head 10 has a plurality of ink ejection openings (nozzle holes) in the main scanning direction. And are mounted with the ink droplet ejection direction facing downward. In addition, each ink cartridge 11 for supplying ink of each color to the head 10 is replaceably mounted on the carriage 9.
The ink cartridge 11 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body. Thus, the ink supplied to the inkjet head is maintained at a slight negative pressure. Further, although the heads 10 of the respective colors are used here as the recording heads, a single head having nozzle holes for ejecting ink droplets of the respective colors may be used.

  Here, the carriage 9 is slidably fitted to the main guide rod 7 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the secondary guide rod 8 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 9 in the main scanning direction, a timing belt 15 is stretched between a driving pulley 13 and a driven pulley 14 that are rotationally driven by a main scanning motor 12. The carriage 9 is reciprocally driven by forward and reverse rotations of the main scanning motor 12.

On the other hand, in order to convey the paper P set in the paper feeding cassette 4 to the lower side of the head 10, the paper feeding roller 16 and the friction pad 17 for separating and feeding the paper P from the paper feeding cassette 4 and the paper P are guided. A guide member 18, a transport roller 19 that reverses and transports the fed paper P, a transport roller 20 that is pressed against the peripheral surface of the transport roller 19, and a leading end that defines a feed angle of the paper P from the transport roller 19 A roller 21 is provided. The transport roller 19 is rotationally driven by a sub-scanning motor 22 through a gear train.
A printing receiving member 23 is provided as a paper guide member for guiding the paper P fed from the transport roller 19 on the lower side of the recording head 10 corresponding to the range of movement of the carriage 9 in the main scanning direction. A conveyance roller 24 and a spur 25 that are rotationally driven to send the paper P in the paper discharge direction are provided on the downstream side of the printing receiving member 23 in the paper conveyance direction, and the paper P is further delivered to the paper discharge tray 6. A roller 26 and a spur 27, and guide members 28 and 29 that form a paper discharge path are disposed.
At the time of recording, the recording head 10 is driven according to the image signal while moving the carriage 9, thereby ejecting ink onto the stopped paper P to record one line. Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the paper P reaches the recording area, the recording operation is terminated and the paper P is discharged.

Further, a recovery device 30 for recovering the ejection failure of the head 10 is disposed at a position outside the recording area on the right end side in the moving direction of the carriage 9. The recovery device 30 includes a cap unit, a suction unit, and a cleaning unit. The carriage 9 is moved to the recovery device 30 side during printing standby and the head 10 is capped by the capping means, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.
When ejection failure occurs, the ejection port (nozzle hole) of the head 10 is sealed by the capping unit, and bubbles and the like are sucked out together with the ink from the ejection port by the suction unit through the tube. Etc. are removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.
In this ink jet recording apparatus, since the ink jet head driven by the waveform having the reverse polarity waveform of Examples 1 to 5 described below is mounted, there is no ink droplet ejection failure due to vibration plate drive failure, and displacement is not caused. Since fluctuations are also suppressed, stable ink droplet ejection characteristics can be obtained, and image quality can be improved.

Hereinafter, a configuration of a droplet discharge head according to an embodiment of the present invention that can be applied to the ink jet recording apparatus illustrated in FIGS. 1 and 2 will be described.
The droplet discharge head changes the volume of the pressure chamber by pressure generating means such as a piezoelectric actuator, and discharges liquid such as ink supplied into the pressure chamber as droplets from the nozzle holes, thereby recording paper such as paper Record an image on
3 and 4 are cross-sectional views showing a schematic configuration of the droplet discharge head according to the present embodiment. FIG. 3 shows a droplet discharge head of one nozzle. FIG. 4 shows a plurality of nozzle holes and each nozzle hole. It is a figure which shows the droplet discharge head which has a some corresponding | compatible pressure chamber.

The droplet discharge head 40 shown in FIGS. 3 and 4 mainly includes a piezoelectric actuator 50 as an electro-mechanical conversion element and one (FIG. 3) or a plurality (FIG. 4) of nozzle holes 61 that discharge droplets. The nozzle plate (nozzle substrate) 60 formed with the pressure chamber 71, the pressure chamber 71 communicating with the nozzle hole 61, respectively, constitute the pressure chamber substrate 70, the wall surface (bottom surface) of the pressure chamber, and vibrate as the piezoelectric actuator deforms. Thus, a diaphragm 80 for changing the volume of the pressure chamber 71 is provided.
In the case shown in FIG. 4, an adhesion layer 90 is interposed between the pressure chamber substrate 70 and the diaphragm 80. This adhesion layer will be described later.
As shown in FIGS. 3 and 4, the piezoelectric actuator 50 includes an upper electrode 51, an electro-mechanical conversion film (piezoelectric body) 52, and a lower electrode 53.
3 and 4, the droplet discharge head 40 includes liquid supply means for supplying a liquid to a liquid chamber (pressure chamber) 71 (not shown), a flow path, and fluid resistance.

FIG. 5 is a diagram showing a processing system for driving the piezoelectric actuator in the droplet discharge head of the present embodiment.
The droplet discharge head 40 or the above-described ink jet recording apparatus main body 1 includes a drive IC 55 for applying a drive voltage for driving the piezoelectric actuator 50.
Further, the apparatus main body 1 includes a control unit Ctr that controls the drive IC.
FIG. 5 illustrates the case of a plurality of electro-mechanical conversion membranes corresponding to a plurality of liquid chambers (in the case of FIG. 4). However, the single nozzle hole shown in FIG. Needless to say, the present invention is also applicable to a droplet discharge head having a liquid chamber.

The drive IC 55 that drives the piezoelectric actuator 50 applies the reference voltage Vb to the common electrode (lower electrode) 53 and applies the drive voltage Va to the individual electrode (upper electrode) 51. The electromechanical conversion film 52 is deformed based on a potential difference represented by | Va−Vb |. The deformation of the electro-mechanical conversion film 52 is transmitted to the pressure chamber 71 via the diaphragm 80 shown in FIGS. 3 and 4, and ink is ejected from the nozzle holes 61 as ink droplets by the pumping action.
In this embodiment, the signal waveform for recovering the displacement amount of the electro-mechanical conversion film 52 is applied by control by the control unit Ctr that controls the drive IC 55.
The control unit Ctr includes, for example, at least a CPU that executes instructions, a ROM that stores a control program, and a RAM as a work area that expands the control program and temporary data for execution by the CPU.
The application of the signal waveform described below is realized by the control of the drive IC 55 by the CPU according to the control program.

Here, a manufacturing method of the droplet discharge head of this embodiment will be described.
FIG. 6 is a diagram showing the arrangement relationship of the substrates or thin films constituting the droplet discharge head of this embodiment.
As shown in FIG. 6, the electro-mechanical conversion element according to this embodiment includes a substrate material 100, a film formation diaphragm material 101, a first electrode material 102, an electro-mechanical conversion film material 103, and a second electrode material. 104.

[Pressure chamber substrate]
The substrate material 100 is a substrate that constitutes the pressure chamber substrate 70 shown in FIGS. 3 and 4, and a silicon single crystal substrate is preferably used, and usually has a thickness of 100 to 600 μm.
There are three types of plane orientations of silicon single crystals: (100), (110), and (111). In the semiconductor industry, silicon single crystals with plane orientations of (100) and (111) are generally widely used. Has been.
Also in this embodiment, a single crystal substrate mainly having a (100) plane orientation is mainly used.
Further, when the pressure chamber 71 as shown in FIGS. 3 and 4 is manufactured, the silicon single crystal substrate 100 is processed using etching. In this case, as an etching method, anisotropic etching is used. Is generally used.
Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure.

For example, in anisotropic etching immersed in an alkaline solution such as KOH (potassium hydroxide), the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Therefore, while a structure having an inclination of about 54 ° can be produced in the plane orientation (100), a deep groove can be dug in the plane orientation (110), so that the arrangement density is increased while maintaining rigidity. I know you can.
Therefore, it is possible to use a silicon single crystal substrate having a (110) plane orientation as this configuration. However, in this case, since SiO ₂ which is a mask material at the time of etching is also etched, this area is also used with attention.

[Diaphragm]
As shown in FIGS. 3 and 4, the diaphragm 80 receives the force generated by the electromechanical conversion film 52, and the base (the diaphragm 80) is deformed and displaced to discharge ink droplets in the pressure chamber.
Therefore, it is preferable that the base has a predetermined strength. Examples of the diaphragm material 101 include those prepared by CVD (Chemical Vapor Deposition) using Si, SiO ₂ , or Si ₃ N ₄ .
Moreover, it is preferable to select a material close to the linear expansion coefficient of the lower electrode (common electrode) 53 and the electromechanical conversion film 52 shown in FIGS. 3 and 4 as the diaphragm material 101.

In particular, as the electro-mechanical conversion film 52, since PZT (Lead Titanate Zirconate) is generally used as the electro-mechanical conversion film material 102 (described later), the linear expansion coefficient is 8 × 10. ^As a linear expansion coefficient close to ⁻⁶ (1 / K), a material having a linear expansion coefficient of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ is preferable, and more preferably 7 × 10 ^{−6 to} 9 × 10 ⁻⁶ . A material having a linear expansion coefficient is more preferable.
Specific materials having a thermal expansion coefficient close to that of PZT include aluminum oxide, zirconium oxide, iridium oxide, ruthenium oxide, tantalum oxide, hafnium oxide, osmium oxide, rhenium oxide, rhodium oxide, palladium oxide, and compounds thereof. The diaphragm 80 using these materials can be manufactured by a spin coater using a sputtering method or a Sol-Gel method.
As a film thickness of the diaphragm 80 (diaphragm material 101), 0.1-10 micrometers is preferable and 0.5-3 micrometers is still more preferable. If the film thickness is smaller (thin) than this range, the processing of the pressure chamber 71 as shown in FIGS. 3 and 4 becomes difficult, and if it is larger (thick) than this range, the vibration plate 80 itself is difficult to deform and displace. Discharge becomes unstable.

[Upper and lower electrodes]
As the first electrode material 102 to be the upper electrode (individual electrode) and the second electrode material 104 to be the lower electrode (common electrode), platinum having high heat resistance and low reactivity has been conventionally used as a metal material. However, it may not be said that it has sufficient barrier properties against lead, and platinum group elements such as iridium and platinum-rhodium, and alloy films thereof can also be used.
Further, when platinum is used, since the adhesion with the diaphragm 80 (especially SiO ₂ ) is poor, the adhesion layer 90 is first formed of Ti, TiO ₂ , Ta, Ta ₂ O ₅ , Ta ₃ N ₅ or the like. (FIG. 4) is preferably laminated.
As a method for producing each electrode, vacuum film formation such as sputtering or vacuum deposition is generally used. The film thickness is preferably 0.05 to 1 μm, and more preferably 0.1 to 0.5 μm.
In addition, because of concerns over the fatigue characteristics of the electro-mechanical conversion film 52 over time, the first electrode (lower electrode 53), the electro-mechanical conversion film 52, the electro-mechanical conversion film 52, and the second electrode (upper part). It is preferable to laminate a conductive oxide such as SrRuO ₃ or LaNiO ₃ as an electrode portion between the electrode 51).

[Electro-mechanical conversion film (piezoelectric material)]
As described above, PZT is mainly used as the electro-mechanical conversion film 52.
PZT is a solid solution of lead zirconate (PbTiO ₃ ) and lead titanate (PbTiO ₃ ), and the characteristics differ depending on the ratio.
Generally, excellent piezoelectric characteristics are exhibited with a composition in which the ratio of PbZrO ₃ and PbTiO ₃ is 53:47.
As the shows the PZT when the chemical formula _{Pb (Z r0.53, Ti 0.47)} O 3 becomes, generally indicated as PZT (53/47).
The other material of the electro-mechanical conversion film 52 is described by the general formula ABO ₃ , and A = Pb, Ba, Sr, B = Ti, Zr, Sn, Ni, Zn, Mg, and Nb as a main component. Applicable.
The specific description is (Pb _1-x , Ba _x ) (Zr, Ti) O ₃ , (Pb) (Zr _x , Ti _y , Nb _1-xy ) O ₃ . This shows a case where Pb at the A site is partially substituted with Ba and a case where Zr and Ti at the B site are partially substituted with Nb.
Such replacement is performed by material modification for improving the displacement characteristics of PZT. Examples of oxides other than PZT include barium titanate and bismuth ferrate.

The electro-mechanical change film 52 can be manufactured by a spin coater using a sputtering method or a Sol-Gel method. In that case, since patterning is required, a desired pattern is obtained by photolithography etching or the like.
When PZT is produced by the Sol-Gel method, a PZT precursor solution can be produced by using lead acetate, zirconium alkoxide, and titanium alkoxide compounds as starting materials and dissolving them in methoxyethanol as a common solvent to obtain a uniform solution. . Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of acetylacetone, acetic acid, diethanolamine or the like may be added to the precursor solution as a stabilizer.
When a PZT film is obtained on the entire surface of the base substrate, it is obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since the transformation from the coating film to the crystallized film involves volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a crack-free film.
The film thickness of the electromechanical conversion film 52 is preferably 0.5 to 5 μm, and more preferably 1 μm to 2 μm. If it is smaller than this range, it will not be possible to generate a sufficient displacement, and if it is larger than this range, many layers will be laminated, resulting in an increase in the number of steps and a longer process time.

  According to the present invention, the piezoelectric actuator 50 can be formed by a simple manufacturing process (and having performance equivalent to that of bulk ceramics), and the etching plate is removed from the back surface for forming the pressure chamber, and the nozzle plate having the nozzle holes is formed. The liquid discharge head is completed by bonding.

Examples of the present invention will be described in detail below.
[Example 1]
First, the piezoelectric actuator 50 was produced as follows.
A thermal oxide film (film thickness: 1 μm) as a vibration plate material 101 as a vibration plate 80 is formed on a silicon wafer as a substrate material 100 as a pressure chamber substrate 70, and a titanium film (film thickness: 50 nm) as an adhesion layer 90 Formed.
Subsequently, as the first electrode material 102 to be the lower electrode 53, a platinum film (film thickness 250 nm) and a SrRuO 3 film (film thickness 50 nm) were sequentially formed by sputtering.
The titanium film serves as an adhesion layer 90 between the thermal oxide film and the platinum film.
The substrate was heated at 550 ° C. during the sputtering film formation for obtaining the lower electrode 53.

Next, a solution prepared with a composition ratio of Pb: Zr: Ti = 110: 53: 47 was prepared as the electro-mechanical conversion film material 103 to be the electro-mechanical conversion film 52.
For the synthesis of a specific precursor coating solution, lead acetate trihydrate, isopropoxide titanium, and isopropoxide zirconium were used as starting materials.
The crystal water of lead acetate was dehydrated after dissolving in methoxyethanol.
The amount of lead is excessive with respect to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment.
Isopropoxide titanium and isopropoxide zirconium were dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction were advanced, and the PZT precursor solution was synthesized by mixing with the above-mentioned methoxyethanol solution in which lead acetate was dissolved.

The PZT concentration was 0.5 mol / liter. Using this PZT precursor solution, a film was formed by spin coating, and after film formation, 120 ° C. drying → 500 ° C. thermal decomposition was performed.
After thermal decomposition treatment of the third layer, crystallization heat treatment (temperature: 750 ° C.) was performed by RTA (Rapid Heat Treatment).
At this time, the film thickness of PZT was 240 nm. This process was performed a total of 8 times (24 layers) to obtain a PZT film thickness of about 2 μm.

Next, as the second electrode material 104 to be the second electrode 51, an SrRuO 3 film (film thickness 40 nm) and a platinum film (film thickness 125 nm) were sequentially formed by sputtering.
Film formation was performed at a substrate temperature of 300 ° C. during the sputtering film formation.
The SrRuO 3 film was post-annealed at 550 ° C./300 s in an oxygen atmosphere by RTA treatment.
Thereafter, a photoresist was formed by spin coating, a resist pattern was formed by ordinary photolithography, and then a pattern was formed using an ICP (inductively coupled plasma) etching apparatus.

Next, in order to form the subsequent pressure chamber 71, the silicon single crystal substrate 100 was polished by a known technique so as to have a desired thickness t (for example, a thickness of 80 μm).
Etching may be used in addition to the polishing method. Next, the partition walls other than the pressure chamber 71 are covered with a resist by a lithography method. Thereafter, anisotropic wet etching was performed with an alkaline solution (KOH solution or TMHA solution) to form a pressure chamber 71, and a piezoelectric actuator 50 as shown in FIGS. 3 and 4 and a liquid discharge head constituted by the piezoelectric actuator 50 were produced. .

FIG. 7 is a diagram showing a typical PE hysteresis loop of the electromechanical conversion element (piezoelectric actuator) 50 in the liquid droplet ejection head according to the present embodiment manufactured by the above procedure.
The coercive electric field of the piezoelectric actuator 50 is about 20 kV / cm as shown in FIG. The coercive electric field means the strength of an electric field that reverses the sign (direction) of polarization in the piezoelectric body.
Variation evaluation of the displacement amount was performed on the piezoelectric actuator 50 of the droplet discharge head prepared as described above.

FIG. 8 is a diagram showing a voltage waveform applied to the piezoelectric actuator 50 in the present embodiment.
As shown in FIG. 8, with respect to the drive waveform F having the maximum value of voltage V1, the voltage -V2 having the opposite polarity to the voltage V1 of the drive waveform F that does not exceed the voltage corresponding to the coercive electric field of the electromechanical conversion film 52 is obtained. Polarity waveform R is applied.
With regard to the applied voltage waveform shown in FIG. 8, in [Example 1], the electric field strength V1 exceeding the coercive electric field ((1) in FIG. 7) is 150 kV / cm by the control of the control unit Ctr in accordance with the control program described above. After applying the drive pulse waveform F (drive voltage Va) for T1 = 500 ms, the reverse polarity pulse waveform R having the opposite polarity to the drive waveform F not exceeding the coercive electric field V2 = −15 kV / cm was applied for T2 = 500 ms. . That is, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied.

The fall and rise of the reverse polarity waveform R at this time were defined by a half-cycle sine wave. The half-cycle sine wave here was derived from the meniscus natural oscillation period Tc at the liquid level of the nozzle hole of the droplet discharge head.
The falling and rising of the reverse polarity waveform R do not necessarily have to be derived from the meniscus natural vibration period Tc. However, in order to avoid a load on the piezoelectric body for the reason described later, it is set based on the meniscus natural vibration period Tc. It is preferable to do.

FIG. 9 is a graph showing the relationship between the driving voltage and the displacement amount of the piezoelectric element, and the relationship between the meniscus natural vibration period Tc and the reverse polarity waveform R.
As shown in FIG. 9, the fall timing (time) and rise timing (time) of the pulse of the reverse polarity waveform R are set so as to substantially coincide with the waveform of the sine wave 110 having the meniscus natural vibration period.
The fall of the reverse polarity waveform R is a section of the angular frequency π / 2 to 3π / 2 when the initial phase is 0 in the sine wave 110 having the meniscus natural oscillation period Tc shown in FIG. A section of π / 2 to π / 2 is preferable.
The meniscus natural vibration period Tc is derived by vibration evaluation or an equivalent circuit method as shown in FIG.
In the pulse waveform of the reverse polarity waveform of [Example 1], the fall time T _f and the rise time Tr are 3.4 μs which is an integral multiple of the meniscus natural vibration period, and the pulse width Tw is also an integral multiple of the meniscus natural vibration period. It was 3.4 μs.
Note that the number of pulse application of the reverse polarity pulse waveform R is desirably 1000 times or more.

[Example 2]
Using the same droplet discharge head as in Example 1, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied. Specifically, for the applied voltage waveform shown in FIG. 8, after applying a drive pulse waveform with an electric field strength V1 = 150 kV / cm for T1 = 500 ms, a reverse polarity pulse waveform with an electric field strength V2 = −5 kV / cm is applied with T2 = 500 ms. Applied. The pulse shape of the reverse polarity waveform R at this time is as follows: the fall time T _f , the rise time Tr is 3.4 μs which is an integral multiple of the meniscus natural vibration period, and the pulse width Tw is 3.4 μs which is an integral multiple of the meniscus natural vibration period. A pulse waveform was used.

[Example 3]
Using the same droplet discharge head as in Example 1, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied. Specifically, with respect to the applied voltage waveform shown in FIG. 8, after applying a driving waveform F with an electric field strength V1 = 150 kV / cm for T1 = 900 ms, the reverse of the pulse shape of Example 1 with an electric field strength V2 = −15 kV / cm. A polarity waveform was applied at T2 = 100 ms. In the pulse waveform of the reverse polarity waveform R at this time, the falling time T _f and the rising time _Tr are 3.4 μs which is an integral multiple of the meniscus natural vibration period, and the pulse width Tw is also an integral multiple of the meniscus natural vibration period. 4 μs.

[Example 4]
Using the same droplet discharge head as in Example 1, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied. Specifically, with respect to the applied voltage waveform shown in FIG. 8, a drive waveform F with an electric field strength V1 = 150 kV / cm is applied for T1 = 500 ms, and then a reverse polarity waveform with an electric field strength V2 = −15 kV / cm is applied with T2 = 500 ms. did.
In the pulse waveform of the reverse polarity waveform R at this time, the fall time T _f and the rise time _Tr are both 3.4 μs which is an integral multiple of the meniscus natural vibration period, and the pulse width Tw is 1 which is a half integer multiple of the meniscus natural vibration period. The pulse waveform was 7 μs.

[Example 5]
Using the same droplet discharge head as in Example 1, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied. Specifically, after applying a driving waveform F having an electric field strength V1 = 150 kV / cm for T1 = 500 ms, a reverse polarity waveform R having an electric field strength V2 = −15 kV / cm was applied for T2 = 500 ms. The pulse waveform of the reverse polarity waveform R at this time is a pulse waveform having a falling time T _f , a rising time Tr of 11.7 μs, and a pulse width Tw of 1.7 μs.

[Comparative Example 1]
Using the same droplet discharge head as in [Example 1], a drive waveform F having an electric field strength of 150 kV / cm exceeding the coercive electric field was applied for 500 ms. The reverse polarity waveform R after the drive waveform F is not applied.
[Comparative Example 2]
Using the same droplet discharge head as in Example 1, a waveform having a combination of the drive waveform F and the reverse polarity waveform R as one sequence was applied. That is, after applying a driving waveform F with an electric field strength V1 = 150 kV / cm for T1 = 500 ms, a reverse polarity waveform R with an electric field strength V2 = −15 kV / cm is set to a rise time T _f and a fall time Tr of 1 μs, and a pulse width. Was applied with a waveform of T2 = 500 ms.
[Comparative Example 3]
The same droplet ejection head as in Example 1 was used, and a waveform having a combination of the driving waveform F and the reverse polarity DC bias as one sequence was applied. That is, after applying a driving waveform F having an electric field strength V1 = 150 kV / cm for T1 = 500 ms, a reverse polarity DC bias having an electric field strength V2 = −5 kV / cm was applied for T2 = 500 ms.

The following is a table summarizing the details of the drive waveform and the reverse polarity waveform in the above-described examples and comparative examples.
[Table 1]

[Evaluation results]
The displacement amount of the piezoelectric actuator 50 was measured using a laser Doppler vibrometer.
When the absolute value of the initial displacement amount of the piezoelectric actuator 50 was 100%, the change rate of displacement after applying the drive waveform pulse 10 to ¹⁰ times was evaluated.
Here, the number of pulses of the reverse polarity waveform R is not counted, and only the number of pulses of the drive waveform F is counted.

FIG. 10 is a graph showing an evaluation result of displacement fluctuations in the electromechanical conversion element of this embodiment, and FIG. 11 is a diagram showing a change rate of the displacement amount of the piezoelectric body.
Regarding [Example 1] to [Example 5], the variation range of the displacement is all within 3%, and the variation of the displacement of the electromechanical conversion film 52 is suppressed by the reverse polarity waveform R. I understand.
This is because with the application of the drive waveform F, the reverse polarity waveform removes the charges in the electro-mechanical conversion film 52 that are unevenly distributed in the film thickness direction of the electro-mechanical conversion film 52 and trapped.
In addition, since the reverse polarity waveform R does not exceed the coercive electric field, the polarization state of the electromechanical conversion film 52 does not repeat reversal even if long-term driving is performed.
Therefore, the burden on the piezoelectric actuator 50 is small, and a stable displacement can be obtained, and the problem of current increase accompanying polarization reversal in a coercive electric field can be avoided.
By the way, as described above, in the droplet discharge head driving method according to the present invention, the rising waveform and the falling waveform in the reverse polarity waveform are defined as the sine waveform of the meniscus natural vibration period of the droplet discharge head. Yes. This is due to the reason described below.

FIG. 12 shows the displacement amount (a) of the diaphragm when simply applying the reverse polarity pulse and the displacement amount (b) of the diaphragm when applying the reverse polarity pulse considering the meniscus natural vibration period. FIG.
The reverse polarity waveform R shown in FIG. 12A is a simple reverse polarity pulse pattern, and does not consider the meniscus natural vibration period. Therefore, the displacement depending on the meniscus natural vibration period is excited, the vibration plate is displaced with a displacement pattern 111 different from the applied reverse polarity waveform R, and desired for the piezoelectric body (electro-mechanical conversion film 52). It can be seen that no voltage is applied.

On the other hand, the resonance is suppressed in the reverse polarity waveform R that makes the falling and rising using the sine wave of the natural period of the meniscus vibration of FIG.
Accordingly, since the displacement can respond correctly to the applied waveform, the effect of suppressing displacement fluctuation can be fully contributed.
Further, by setting the pulse width of the reverse polarity waveform R to an integer multiple of the meniscus natural oscillation period, in [Example 2], the electric field strength of the reverse polarity waveform R can be made lower than the coercive electric field. The expression of the effect has been achieved.
The upper limit of the electric field strength of reverse polarity is less than the coercive electric field, the lower limit is preferably 20% or more of the coercive electric field, and the upper limit is more preferably 80% of the coercive electric field.

In [Example 3], even if the application time of the reverse polarity waveform R is shortened, the effect can be achieved.
This is because even if the application time of the reverse polarity waveform R is short, the trapped charges can be extracted in the application time of the drive waveform F.
The application time of the reverse polarity waveform R is preferably 50 ms or more, more preferably 100 ms or more.
Further, the variation in displacement is caused by the uneven distribution of trapped charges in the film thickness direction accompanying the application of the drive waveform F.
Therefore, the application time ratio between the drive waveform F and the reverse polarity waveform R is important, and the application time of the reverse polarity waveform R is preferably 0.1 times or more of the application time of the drive waveform F.

In [Embodiment 4] and [Embodiment 5], the pulse shape of the reverse polarity waveform R is manipulated. The effect can be confirmed even when the pulse waveform falls slowly and rises, and a sufficient application time of the reverse polarity waveform R is sufficient.
Even if the pulse width of the reverse polarity waveform R is short, it is effective, but since the charge trapped during driving is extracted by the reverse polarity waveform R, there is a balance with the charge / discharge characteristics of the piezoelectric actuator 50. The width is preferably 1 μsec or more.
In addition, the fall time, rise time, and pulse width of the pulse waveform of the reverse polarity waveform R have a balance with the application time of the reverse polarity waveform, but the fall time and the rise time are meniscus natural vibration periods for suppressing resonance. It is more preferable that the pulse width is an integer multiple and a half integer multiple of ½ times or more of the meniscus natural vibration period.

The evaluation results of each comparative example were as follows.
That is, in [Comparative Example 1] and [Comparative Example 2], the fluctuation range of the displacement is large.
This is because, in [Comparative Example 1], a reverse polarity waveform is not applied, so that charges accumulated during driving cannot be extracted, and the uneven distribution of charges progresses over time.
In [Comparative Example 2], although a reverse polarity DC bias is applied, the displacement varies greatly. In [Comparative Example 3], as shown in FIG. 12, extra vibrations excited by resonance are generated.

As described above, an internal electric field generated in the electro-mechanical conversion film 52 due to the application of the drive waveform is unevenly distributed in the film thickness direction by applying a voltage waveform having a polarity opposite to the voltage direction of the drive waveform when not driving. The internal electric field is generated by the uneven distribution of charges in the film thickness direction of the electro-mechanical conversion film 52 due to driving, and the reverse of this case. By making the voltage intensity of the polar voltage less than the coercive electric field, it is possible to prevent the polarization axis from being reversed when applied more than the coercive electric field.
Further, according to the present invention, the rising and falling waveforms in the reverse polarity pulse waveform are defined by the sine wave having the meniscus natural vibration period, thereby suppressing the forced vibration derived from the internal meniscus natural vibration period. By doing so, the reduction of the electro-mechanical conversion capability can be suppressed by reducing the extra burden applied to the electro-mechanical conversion element.
Needless to say, the driving method of the present invention is applicable not only to an ink jet recording apparatus that ejects ink, but also to other liquid ejecting apparatuses that eject liquid other than ink.
In the above description, the driving method of the piezoelectric body used for the piezoelectric actuator of the droplet discharge device has been described. However, the present invention can also be applied to a driving method of a piezoelectric body (piezoelectric actuator) alone. In that case, it is not necessary to consider the meniscus natural period peculiar to the droplet discharge device.

DESCRIPTION OF SYMBOLS 1 Recording device main body, 2 Printing mechanism part, 4 Paper feed cassette, 5 Tray, 6 Paper discharge tray, 7 Main guide rod, 8 Sub guide rod, 9 Carriage, 10 Recording head, 11 Ink cartridge, 12 Main scanning motor, 13 Drive pulley, 14 driven pulley, 15 timing belt, 16 feed roller, 17 friction pad, 18 guide member, 19 transport roller, 20 transport roller, 21 tip roller, 22 sub-scanning motor, 23 printing receiving member, 24 transport roller , 25 spur, 26 discharge roller, 27 spur, 28 guide member, 30 recovery device, 40 inkjet head, 50 piezoelectric actuator, 51 upper electrode, 52 mechanical conversion film, 53 lower electrode, 60 nozzle plate, 61 nozzle hole, 70 Pressure chamber substrate, 71 pressure chamber, 80 diaphragm, 90 Adhesion layer, 100 Silicon single crystal substrate material, 101 Film-forming diaphragm material, 102 First electrode material, 103 Mechanical conversion film material, 104 Second electrode material

JP-A-6-342946 JP 2003-80698 A

Claims (10)

A driving method of a piezoelectric body that is deformed by applying a voltage,
After applying a first waveform whose electric field strength exceeds the coercive electric field of the piezoelectric material to the piezoelectric body, a pulse having a reverse polarity to the first waveform and an electric field strength less than the coercive electric field A method for driving a piezoelectric body, comprising applying a second waveform which is a waveform. A method of driving a droplet discharge head, which has a piezoelectric body that is deformed by application of a voltage, and discharges droplets from nozzle holes that communicate with the liquid chamber by a change in the volume of the liquid chamber accompanying the deformation of the piezoelectric body. There,
After applying a first waveform whose electric field strength exceeds the coercive electric field of the piezoelectric material to the piezoelectric body, a pulse having a reverse polarity to the first waveform and an electric field strength less than the coercive electric field A driving method of a droplet discharge head, wherein a second waveform which is a waveform is applied. The method for driving a droplet discharge head according to claim 2,
The method of driving a droplet discharge head, wherein the electric field intensity of the second waveform is 20% or more of the coercive electric field. In the driving method of the droplet discharge head according to claim 2 or 3,
The method of driving a droplet discharge head, wherein the second waveform is based on a sine wave that indicates a meniscus natural oscillation period of the droplet discharge head when the pulse waveform falls and rises. The method of driving a droplet discharge head according to claim 4,
The fall time of the second waveform is set to an interval of the sine wave angular frequency π / 2 to 3π / 2,
The method of driving a droplet discharge head, wherein the rise time of the second waveform is set in an interval of an angular frequency of the sine wave from −π / 2 to π / 2. In the driving method of the droplet discharge head according to claim 4 or 5,
The method of driving a droplet discharge head, wherein the fall time and the rise time of the second waveform are an integral multiple of the meniscus natural vibration period. The method for driving a droplet discharge head according to any one of claims 4 to 6,
The method of driving a droplet discharge head, wherein the pulse width of the second waveform is an integral multiple of the meniscus natural vibration period. The method for driving a droplet discharge head according to any one of claims 4 to 6,
The method of driving a droplet discharge head, wherein the pulse width of the second waveform is a half integer multiple of the meniscus natural vibration period. A piezoelectric body that deforms when a voltage is applied thereto, a liquid chamber whose volume changes due to the deformation of the piezoelectric body, and a liquid that communicates with the liquid chamber and changes in volume of the liquid chamber as droplets. A nozzle hole for discharging, and a waveform applying means for applying a driving waveform to the piezoelectric body,
9. The liquid droplet ejection head according to claim 2, wherein the waveform applying unit drives the piezoelectric body by a method for driving the liquid droplet ejection head.   An image recording apparatus comprising the droplet discharge head according to claim 9.

Images